An experimental animal model has been established in which carcinogenesis was induced by dietary nitrite given in association with anion exchange resin as a close analogy to a natural process where nitrite intake occurs in human populations. In order to exploit the model, several lines of experimental approach are adopted: 1) germfree technique is incorporated so that the indispensable role of intestinal flora is established for carcinogenesis due to dietary nitrite and the technique of monocontamination is utilized to make a correlation between the in vitro nitrosation activity of several bacterial species and their carcinogenic activity in vivo, 2) for elucidation of carcinogenic processes with a special reference to organ specificity, modification of following experimental variables are intended in addition to the basic nitrite resin diet, animal species and strains, dietary components, dose and time course of resin administration, hormonal disturbances, synergistic action of X ray, promotors and inhibitors, and alteration of physiological and biochemical functions.